CONVERGENCE OF LARYNGEAL AFFERENTS WITH DIFFERENT NATURES UPON CAT NTS NEURONS

To clarify the convergence of laryngeal afferents within the nucleus t ractus solitarius (NTS) in the cat, we examined in the medulla the res ponse characteristics of superior laryngeal nerve (SLN) fibers and NTS neurons to mechanical and chemical stimulation applied to laryngeal m ucosa by extracellular recordings. The response was recorded in 75 SLN primary afferent fibers (PAFs) and 92 NTS neurons. PAFs of the SLN co nsisted of numerous monomodal mechanosensitive fibers and a small numb er of chemosensitive and polymodal fibers. On the other hand, the majo rity of NTS neurons had a polymodal nature. Thus, laryngeal informatio n is considered to be integrated in modality into NTS neurons. AII mec hanosensitive fibers received information from a small restricted fiel d in the larynx. On the contrary, each NTS neuron responded to mechani cal stimulation over a wide laryngeal field, indicating that informati on from different sites spatially converge on NTS neurons. Our results suggest that caudal NTS neurons play a cardinal role in integrating l aryngeal afferents, which are thought to elicit laryngeal reflexes.